This application claims the priority of German Application No. 100 36 789.5, filed Jul. 28, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for determining the traffic state in a traffic network with effective bottlenecks.
A traffic state determining method of this type is described in the German Patent Application 199 44 075.1 by the applicant with earlier priority, the contents of which are entirely incorporated herein by reference.
Methods for monitoring and forecasting the traffic state on, for example, road traffic networks are known in different forms and are particularly also of interest for various telematic applications in vehicles. An objective of these methods is to acquire an at least qualitative description of the traffic state at a respective measuring point and its surroundings from traffic data recorded at traffic measuring points. Possible measuring points in such a case are both measuring points which are installed in a stationary fashion and mobile measuring points, the latter being in particular in the form of measuring vehicles, referred to as xe2x80x9cfloating carsxe2x80x9d, which move along in the traffic.
In order to arrive at a qualitative description of the traffic state it is known to classify the latter into various, individually identifiable state phases, specifically into the xe2x80x9cfreely flowing trafficxe2x80x9d, xe2x80x9csynchronized trafficxe2x80x9d and xe2x80x9ccongestionxe2x80x9d phases, it being possible for the xe2x80x9csynchronized trafficxe2x80x9d phase to contain what is referred to as xe2x80x9cpinch regionsxe2x80x9d in which vehicles can travel only at very low speeds and brief congestion states form spontaneously and can migrate and grow upstream so that persistent congestion states can develop from them. These congestion states then form regions of xe2x80x9cwide moving jamxe2x80x9d; see the above German Patent Application 199 44 075.1 with earlier priority from the same company, and the literature cited there, on this subject area of state phases.
The term xe2x80x9ceffective bottlenecksxe2x80x9d refers here to points in the traffic network at which given an appropriate traffic volume a boundary or edge which persists on a localized basis over a specific time period forms between downstream freely flowing traffic and upstream synchronized traffic. The formation of such effective bottlenecks is determined frequently, if not exclusively, by corresponding topographic conditions of the road network, such as bottlenecks at which the number of useable lanes is reduced, lanes entering a road, a bend, a positive incline, a negative incline, splitting up of a carriageway into a plurality of carriageways or exits. Effective bottlenecks can, however, also be caused by, for example, temporary traffic disruption such as bottlenecks which move slowly in comparison to the average vehicle speed in freely flowing traffic, for example roadworks vehicles, or by road accidents.
As is described in detail in the German Patent Application 199 44 075.1 with earlier priority, the traffic state upstream of effective bottlenecks can be classified into various patterns of dense traffic which are composed of a typical sequence of the aforementioned individually identifiable dynamic state phases or regions which are formed therefrom. Thus, at first a region of synchronized traffic is typically formed upstream of an effective bottleneck, it being possible for the upstream by a pinch region ahead of which a region of widespread moving congestion can form. Associated with each such pattern of dense traffic upstream of an effective bottleneck is a corresponding profile of the traffic parameters, such as the time/location profile of the vehicle speed within the pattern, which are taken into account for determining the state phases. If a pattern of a first effective bottleneck reaches the location of a second effective bottleneck, what is referred to as an extensive pattern of dense traffic, which includes a plurality of effective bottlenecks, is formed. Such extensive patterns have a typical sequence of different traffic state phases and associated traffic parameter profiles.
In so far as effective bottlenecks are determined by the properties of the traffic route network itself, such as entries, exits, route sections with a positive incline, bends, splitting up of carriageways and confluences of carriageways, the local positions of such topographic route features can be stored without difficulty at the vehicle end or in a traffic control centre, for example together with other route network data in the form of what is referred to as a digital route network map.
It is known that stored traffic data which is required empirically or in other ways can be used to forecast traffic states on the traffic network, i.e. predicted for a future time. A known forecasting method is referred to as load curve forecasting in which currently measured traffic data is compared with stored load curve traffic data and a load curve which fits best is determined therefrom and used as the basis for estimating the future traffic state, see for example German Laid-open Publication DE 197 53 034 A1. Further traffic state forecasting methods which may also make use, inter aila, of FCD (floating car data) traffic data are described in German Laid-open Publications DE 197 25 556 A1, DE 197 37 440 A1, DE 197 54 483 A1 and EP 0 902 405 A2, and in the Patent DE 195 26 148 C2.
The invention is based on the technical problem of making available a method of the type mentioned at the beginning with which the current traffic state can be determined comparatively reliably, specifically also in the region upstream of effective bottlenecks, so that, on this basis reliable traffic forecasts are also possible, when necessary.
The invention solves this problem by providing a method characterized in particular by the fact that currently acquired FCD traffic data is used to detect patterns of dense traffic at effective bottlenecks. To do this, the FCD traffic data includes at least information relating to the location and the speed, preferably relating to the time-dependent and location-dependent speed profile, of the respective traffic data-recording FCD vehicle, the FCD traffic data being acquired for a respective route section by an FCD vehicle at specific time intervals and/or by a plurality of FCD vehicles travelling along this route section at time intervals.
By reference to the FCD traffic data which is recorded by the FCD vehicle or vehicles, it is then determined for the respective route section whether an effective bottleneck is present, i.e. a boundary or edge remaining localized over a certain time period between downstream freely flowing traffic and upstream synchronized traffic. This can be detected, for example, from the fact that the vehicle speeds reported by the FCD vehicle or vehicles in the respective route section upstream of the effective bottleneck drop below an average speed value which is typical of the state of freely flowing traffic.
If an effective bottleneck is detected in this way, the currently recorded FCD traffic data continues to be evaluated to determine whether it is assigned a pattern of dense traffic which fits it upstream of the effective bottleneck. This is then considered as the currently present pattern of dense traffic at the respective effective bottleneck. In this way, the current traffic state in this region is determined, which can be used, for example, for a traffic forecast by means of a load curve forecast or some other forecasting technique.
According to another aspect, a detection is made by using the currently recorded FCD traffic data to determine whether a region of xe2x80x9cwide moving jamxe2x80x9d has broken away from its pattern of dense traffic at whose upstream end it has come about, which is the case if the reported vehicle speeds downstream of this region do not behave as in the pinch region, but rather, for example, as in the region of freely flowing traffic.
Another method according to the present invention permits the specific detection of entry-like or exit-like effective bottlenecks by virtue of the fact that the reported vehicle speeds rise over or before the actual location of the corresponding change in the route topography which is present, for example, as information stored in a digital route map. Another method permits the detection of temporary bottlenecks which are not caused topographically but, for example, are due to road accidents.
Another aspect makes it possible to detect extended patterns of dense traffic in which, in each case, two or more effective bottlenecks are involved.
Another object of the invention is to specifically permit the detection of the boundary between the region of xe2x80x9cwide moving jamsxe2x80x9d and the xe2x80x9cpinch regionxe2x80x9d in a pattern of dense traffic. Analogously, another developed method permits the detection of the boundary between the xe2x80x9cpinch regionxe2x80x9d and the region of xe2x80x9csynchronized trafficxe2x80x9d in a pattern of dense traffic, and a preferred method of the present invention allows for the detection of the boundary between the region of xe2x80x9cfreely flowing trafficxe2x80x9d and the xe2x80x9cpinch regionxe2x80x9d.
Another aspect of the present invention permits the current density of the traffic to be determined from the recorded FCD traffic data for the various detected traffic state phases comprising xe2x80x9cfreely flowing trafficxe2x80x9d, xe2x80x9csynchronized trafficxe2x80x9d and xe2x80x9cpinch regionxe2x80x9d by reference to associated travel times derived from the FCD traffic data. In an analogous fashion, the flow rate is able to be determined for detected regions of congestion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.